Method and system for providing an improved three port wavelength division multiplexer

ABSTRACT

A system and method for providing a wavelength division multiplexer is disclosed. In one aspect, the system and method include providing a housing for the wavelength division multiplexer. The housing includes a first port having a first aperture therein, a second port having a second aperture and a first plurality of apertures therein, and a third port having a third aperture and a second plurality of apertures therein. The second and third apertures are coupled to the first aperture. The first plurality of apertures are disposed symmetrically around the second aperture. The second plurality of apertures are disposed symmetrically around the third aperture. In another aspect, the method and system include providing a wavelength division multiplexer. The wavelength division multiplexer includes a first port including a first collimator, a second port coupled to the first port, and a third port coupled to the first port. The second port includes a second collimator and a first plurality of joints for affixing the second collimator. The first plurality of joints is disposed symmetrically around the second collimator. The third port includes a third collimator and a second plurality of joints for affixing the third collimator. The second plurality of joints is disposed symmetrically around the third collimator.

The present application is a divisional of U.S. Ser. No. 08/918,357filed Aug. 26, 1997 now U.S. Pat. No. 5,946,435.

FIELD OF THE INVENTION

The present invention relates to a method and system for a wavelengthdivision multiplexer ("WDM") and more particularly to a method andsystem for implementing a WDM which provides improved reliability andperformance.

BACKGROUND OF THE INVENTION

A conventional wavelength division multiplexer ("WDM") is used tocombine or separate optical signals having different wavelengths. Forexample, a three port WDM can be used to combine two optical signals orto separate an incoming signal into two components which have twodifferent wavelengths.

In optical communications, conventional WDMs have many applications. Forexample, conventional WDMs are often used in optical amplifiers, inwhich a signal having one wavelength, such as 1550 nanometers ("nm"),can be amplified by combining the signal with a pumping source, forexample, a pumping source having a wavelength of 980 nm or 1480 nm.Another application for WDMs is simultaneous transmission of a pluralityof optical signals over a single fiber. A conventional WDM combines thesignals having wavelengths of 1310 nm and 1550 nm prior to transmissionover the single fiber and separates the signals at the receiver.

A large cost in optical technology is the cost of providing opticalfibers to carry the optical signal between points. To reduce this cost,there is a trend towards carrying more signals on a single fiber ratherthan providing additional fibers. As a result, the demand for WDMs usedto separate or combine such signals has dramatically increased. As thenumber of signals per fiber increases, the wavelength of each signalbecomes closer to the wavelength of neighboring signals. In response tothis decrease in spacing between signals, dense WDMs have beendeveloped. Dense WDMs typically separate or combine optical signalshaving only small differences in wavelength. The difference betweenwavelengths of neighboring signals in a dense WDM is typically less than3.2 nm.

In addition to combining and separating closely spaced signals, WDMsmust be reliable and perform well in the environment in which they areplaced. For example, there are always transmission losses associatedwith a conventional WDM. These transmission losses should be small andremain constant throughout operation of the WDM. However, thetemperature of the environment in which the WDM operates can vary. Thus,a WDM should have a small transmission loss which is relativelyinsensitive to temperature. A WDM should also be reliable. Consequently,Bellcore standards for optical components, which concern the reliabilityof optical components, should also be met.

Although a conventional WDM can separate or combine signals, thereliability and performance of the WDM can be affected by the packagingof the WDM. Typically, in the case of micro-optic WDMs which are basedon collimators and thin-film filters, the collimators of a WDM are heldin place by epoxy. The epoxy may have a temperature dependence and maynot be mechanically reliable. Consequently, the WDM will not havesufficient performance or reliability.

Accordingly, what is needed is a system and method for providing a WDMwhich has improved reliability. The present invention addresses such aneed.

SUMMARY OF THE INVENTION

The present invention provides a method and system for providing amicro-optic wavelength division multiplexer. In one aspect, the systemand method comprise providing a housing for the wavelength divisionmultiplexer. The housing comprises a first port having a first aperturetherein, a second port having a second aperture and a first plurality ofapertures therein, and a third port having a third aperture and a secondplurality of apertures therein. The second and third apertures arecoupled to the first aperture. The first plurality of apertures aredisposed symmetrically around the second aperture. The second pluralityof apertures are disposed symmetrically around the third aperture. Inanother aspect, the method and system comprise providing a wavelengthdivision multiplexer. The wavelength division multiplexer includes afirst port including a first collimator, a second port coupled to thefirst port, and a third port coupled to the first port. The second portincludes a second collimator and a first plurality of joints foraffixing the second collimator. The first plurality of joints isdisposed symmetrically around the second collimator. The third portincludes a third collimator and a second plurality of joints foraffixing the third collimator. The second plurality of joints isdisposed symmetrically around the third collimator.

According to the system and method disclosed herein, the presentinvention increases reliability while keeping a low temperaturedependence, thereby increasing overall system performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional WDM.

FIG. 2a is a block diagram of a side view of one embodiment of a housingin accordance with the method and system.

FIG. 2b depicts one end view of one embodiment of the housing inaccordance with the method and system.

FIG. 2c depicts another end view of one embodiment of the housing inaccordance with the method and system.

FIG. 3 is a block diagram of a WDM in accordance with the method andsystem.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an improvement in micro-opticwavelength division multiplexers ("WDM"). The following description ispresented to enable one of ordinary skill in the art to make and use theinvention and is provided in the context of a patent application and itsrequirements. Various modifications to the preferred embodiment will bereadily apparent to those skilled in the art and the generic principlesherein may be applied to other embodiments. Thus, the present inventionis not intended to be limited to the embodiment shown but is to beaccorded the widest scope consistent with the principles and featuresdescribed herein.

FIG. 1 is a block diagram of a conventional three port WDM 10. Aconventional WDM is used to combine or separate optical signals. Thethree port WDM 10 can be used to combine two optical signals or toseparate an incoming signal into two components. Conventional WDMs cancombine or separate signals having different wavelengths. For example,the three port WDM 10 may separate or combine signals having wavelengthλ1 and λ2, where λ1 and λ2 can be any of a variety of wavelengths.

The conventional three port WDM 10, includes a common port 12 having acollimator 50, a pass port 20 including a collimator 60, and areflection port 30 having a collimator 70. The WDM 10 can be used toseparate a combination signal into its components, a first signal and asecond signal. The first signal and the second signal have wavelengthsλ1 and λ2, respectively. The combination signal enters the WDM 10through fiber 52. The combination signal is transmitted through thecollimator 50 to a narrow band pass filter 42. The filter 42 transmitslight having wavelength λ1. Thus, the first signal is transmittedthrough the filter 42 to the collimator 60 and through the fiber 62. Thesecond signal is reflected to the collimator 70 and through the fiber72. Consequently, the WDM 10 separates the combination signal into itscomponent signals. If the WDM 10 is used to combine two signals, thefirst and second signals would enter through fibers 62 and 72,respectively. The signals would be combined, and the combination signalwould exit the WDM 10 through the fiber 52.

Although the conventional three port WDM 10 can separate or combinesignals, those with ordinary skill in the art will realize that thereliability and performance of the conventional WDM 10 can be adverselyaffected by the packaging of the conventional WDM 10. Typically, thecollimators 50, 60, and 70 of the conventional WDM 10 are held in placeby epoxy (not shown) around the inner surface of the common port 12, thepass port 20 and the reflection port 30, respectively. The epoxy mayhave a temperature dependence and may not be sufficiently mechanicallyreliable. Consequently, the WDM 10 may not have the requisiteperformance, for example exhibiting a large temperature dependence forits transmission loss, or may not have the required reliability.

The present invention provides for a method and system for providing animproved WDM made using soldering technology and a unique housing. Thepresent invention will be described in terms of a three port WDM.However, one of ordinary skill in the art will readily recognize thatthis method and system will operate effectively for other types of WDMs.

To more particularly illustrate the method and system in accordance withthe present invention, refer now to FIGS. 2a-2c depicting one embodimentof a housing 100 for a three port WDM in accordance with the method andsystem. FIG. 2a depicts a side view of the housing 100. The housingincludes a common port 112, a pass port 120, and a reflection port 130.FIG. 2b depicts an end view of the housing 100 from the end includingthe common port 112 and the reflection port 130. FIG. 2c depicts an endview of the housing 100 from the end including the pass port 120. In apreferred embodiment, the housing 100 is made of stainless steel. Inaddition, in a preferred embodiment of the housing 100, the stainlesssteel is gold plated. Stainless steel is used because it is relativelyeasy to solder to, can be gold plated, and has a relatively smallcoefficient of thermal expansion. The housing 100 includes an aperture140 in which a filter (not shown) will be placed. In a preferredembodiment, a holder (not shown) containing the filter will be placed inthe aperture 140.

The housing 100 includes apertures 122, 124, 126, and 128 arrangedsymmetrically around the pass port 120. The housing 100 also includesapertures 132, 134, 136, and 138 arranged symmetrically around thereflection port 130. The apertures 122 through 128 and 132 through 138are used for soldering collimators to the pass port 120 and thereflection port 130.

FIG. 3 depicts one embodiment of a WDM 200 utilizing housing 100 inaccordance with the method and system. Thus, collimators 150, 160, and170 have been placed in the common port 112, the pass port 120, and thereflection port 130, respectively, of the housing 100. The WDM 200includes a filter 142 contained in a holder which has been placed in theaperture 140. The angle at which the filter 142 is held in the aperture140 can be adjusted to ensure the filter 142 only transmits light of thedesired wavelength. In accordance with the method and system, the WDM200 is manufactured by using solder technology to affix certaincomponents to the housing 100.

In one embodiment of the method and system, the collimator 150 isaffixed to the common port 112 using epoxy. Consequently, epoxy joints114 and 116 surround the collimator 150. The diameter of the common port112 very closely matches the diameter of the collimator 150, allowingthe collimator 150 to fit tightly within the common port 112. Thus, itis relatively simple to use epoxy to hold the collimator 150 in place.Similarly, the holder for the filter 142 is held in the aperture 140 byepoxy. However, the remaining collimators 160 and 170 are held in placeby solder, shown in black, which is placed symmetrically around theports 120 and 130, respectively, in apertures 122 through 128 and 132through 138, respectively. In addition, in one embodiment, thecollimators 160 and 170 are also held in place by solder joints 129 and139, respectively.

The apertures 122 through 128 and 132 through 138 and, therefore, thesolder joints made by placing solder in the apertures 122 through 128and 132 through 138 are symmetric. This symmetry and the use of solderin forming the joints allow for greater mechanical stability of thecollimators 160 and 170. In a preferred embodiment, the apertures 122through 128 and 132 through 138 are each placed approximately ninetydegrees apart along the outside surface of the pass port 120 and thereflection port 130, respectively. Although the WDM 200 and housing 100are described as having four symmetric solder joints and four symmetricapertures, respectively, around the reflection port and pass port,nothing prevents the use of another number of symmetric solder joints orapertures, respectively.

Use of soldering technology and symmetric solder joints providesimproved mechanical stability. As a result, the WDM 100 is morereliable. In addition, because the coefficient of thermal expansion ofthe stainless steel housing 100 is relatively low, limiting thetemperature dependence of the behavior of the WDM 200. Thus, performanceof the WDM 200 is improved.

A method and system has been disclosed for an improved WDM. Although thepresent invention has been described in accordance with the embodimentsshown, one of ordinary skill in the art will readily recognize thatthere could be variations to the embodiments and those variations wouldbe within the spirit and scope of the present invention. Accordingly,many modifications may be made by one of ordinary skill in the artwithout departing from the spirit and scope of the appended claims.

What is claimed is:
 1. A housing for use in a wavelength divisionmultiplexer comprising:a first port, the first port having a firstaperture therein; a second port having a second aperture and a firstplurality of apertures therein, the second aperture being coupled to thefirst aperture, the first plurality of apertures being disposedsymmetrically around the second aperture; and a third port having athird aperture and a second plurality of apertures therein, the thirdaperture being coupled to the first aperture, the second plurality ofapertures being disposed symmetrically around the third aperture.
 2. Thehousing of claim 1 wherein the first aperture further includes a firstaxis, and the second aperture further includes a second axis, the secondaxis and the first axis forming substantially a single line.
 3. Thehousing of claim 2 wherein each of the first plurality of aperturesfurther includes a first corresponding axis, the first correspondingaxis of each of the first plurality of apertures being substantiallyperpendicular to the second axis.
 4. The housing of claim 3 wherein thethird aperture further includes a third axis; andwherein each of thesecond plurality of apertures further includes a second correspondingaxis, the second corresponding axis of each of the second plurality ofapertures being substantially perpendicular to the third axis.
 5. Thehousing of claim 4 further comprising:a fourth aperture having a fourthaxis, the fourth aperture being coupled to the first aperture, thefourth axis being substantially perpendicular to the first axis.
 6. Thehousing of claim 5 wherein the first plurality of apertures furthercomprises four apertures separated by approximately ninety degrees. 7.The housing of claim 6 wherein the second plurality of apertures furthercomprises four apertures separated by approximately ninety degrees. 8.The housing of claim 7 wherein the housing further comprises a stainlesssteel housing.
 9. The housing of claim 8 wherein the housing furthercomprises a gold-plated stainless steel housing.
 10. A method ofproviding housing for use in a wavelength division multiplexer, themethod comprising the steps of:providing a first port, the first porthaving a first aperture therein; providing a second port having a secondaperture and a first plurality of apertures therein, the second aperturebeing coupled to the first aperture, the first plurality of aperturesbeing disposed symmetrically around the second aperture; and providing athird port having a third aperture and a second plurality of aperturestherein, the third aperture being coupled to the first aperture, thesecond plurality of apertures being disposed symmetrically around thethird aperture.
 11. The method of claim 10 wherein the first aperturefurther includes a first axis, and the second aperture further includesa second axis, the second axis and the first axis forming substantiallya single line.
 12. The method of claim 11 wherein the step of providingthe second port further comprises the step of:providing a firstplurality of corresponding axes, each of the first plurality ofcorresponding axes corresponding to each of the first plurality ofapertures, each of the first plurality of corresponding axes beingsubstantially perpendicular to the second axis.
 13. The method of claim12 wherein the third aperture further includes a third axis; and whereinthe step of providing the third port further comprises the stepof:providing a second plurality of corresponding axes, each of thesecond plurality of corresponding axes corresponding to each of thesecond plurality of apertures, each of the second plurality ofcorresponding axes being substantially perpendicular to the third axis.14. The method of claim 13 further comprising the step of:providing afourth aperture having a fourth axis, the fourth aperture being coupledto the first aperture, the fourth axis being substantially perpendicularto the first axis.
 15. The method of claim 14 wherein the step ofproviding the first plurality of apertures further comprises the stepof: providing four apertures separated by approximately ninety degrees.16. The method of claim 15 wherein the step of providing the secondplurality of apertures further comprises the step of providing fourapertures separated by approximately ninety degrees.
 17. The method ofclaim 16 wherein the housing further comprises a stainless steelhousing.
 18. The method of claim 17 wherein the housing furthercomprises a gold-plated stainless steel housing.